Integer sequence
An integer sequence is an ordered set of mathematical quantities called terms. A sequence is said to be known if a formula can be given for any particular term using the preceding terms or using its position in the sequence. For example, the sequence 1, 1, 2, 3, 5, 8, 13, ? (the Fibonacci sequence) is formed by adding any two consecutive terms to obtain the next term. The sequence ?1/2, 1, 7/2, 7, 23/2, 17, ? is formed according to the formula (n2 ? 2)/2 for the nth, or general, term. A sequence may be either finite, e.g., 1, 2, 3, ? 50, a sequence of 50 terms, or infinite, e.g., 1, 2, 3, ? , which has no final term and thus continues indefinitely. Special types of sequences are commonly called progressions. The terms of a sequence, when written as an indicated sum, form a series; e.g., the sum of the sequence 1, 2, 3, ? 50 is the series 1 + 2 + 3 + ? + 50. To find information about specific integer sequences the place to go is Neil Sloane's Encyclopedia of Integer Sequences.
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